<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
<div>哈哈哈哈</div>
<script>
  //先选中div,然后通过点击事件来修改文字大小
  let div = document.querySelector('div');
  div.onclick = function(){
    //修改div的元素中文字的大小
    //div.style = 'font-size: 100px';
    div.style.fontSize = '100px';
  }
</script>
</body>
</html>